On Mon, Oct 26, 2020 at 08:57:30AM +0800, yang_y_yi wrote: > At 2020-10-23 22:46:42, "Ananyev, Konstantin" <konstantin.anan...@intel.com> > wrote: > > >> From: yang_y_yi <yang_y...@163.com> > >> Sent: Friday, October 23, 2020 2:18 PM > >> To: Ananyev, Konstantin <konstantin.anan...@intel.com> > >> Cc: dev@dpdk.org; Hu, Jiayu <jiayu...@intel.com>; techbo...@dpdk.org; > >> tho...@monjalon.net; yangy...@inspur.com > >> Subject: Re:RE: [PATCH v2] gso: fix free issue of mbuf gso segments attach > >> to > >> > >> Konstantin, thank you so much for comments, my replies inline, please > >> check them. > >> At 2020-10-22 21:16:43, "Ananyev, Konstantin" > >> <mailto:konstantin.anan...@intel.com> wrote: > >> > > >> >> > >> >> rte_gso_segment decreased refcnt of pkt by one, but > >> >> it is wrong if pkt is external mbuf, pkt won't be > >> >> freed because of incorrect refcnt, the result is > >> >> application can't allocate mbuf from mempool because > >> >> mbufs in mempool are run out of. > >> >> > >> >> One correct way is application should call > >> >> rte_pktmbuf_free after calling rte_gso_segment to free > >> >> pkt explicitly. rte_gso_segment mustn't handle it, this > >> >> should be responsibility of application. > >> > > >> >Probably needs to be stated clearly: > >> >It is a change in functional behaviour. > >> >Without deprecation note in advance. > >> > >> Ok, I'll add such statement in next version. > >> > >> >TB members: please provide your opinion on that patch. > >> > > >> >> > >> >> Fixes: 119583797b6a ("gso: support TCP/IPv4 GSO") > >> >> Signed-off-by: Yi Yang <mailto:yangy...@inspur.com> > >> >> --- > >> >> Changelog: > >> >> > >> >> v1->v2: > >> >> - update description of rte_gso_segment(). > >> >> - change code which calls rte_gso_segment() to > >> >> fix free issue. > >> >> > >> >> --- > >> >> app/test-pmd/csumonly.c | 3 ++- > >> >> doc/guides/prog_guide/generic_segmentation_offload_lib.rst | 7 +++++-- > >> > > >> >I think release notes also have to be updated. > >> > >> Ok, also will update it to reflect this change. > >> > >> > > >> >> lib/librte_gso/rte_gso.c | 9 > >> >> +-------- > >> >> lib/librte_gso/rte_gso.h | 7 +++++-- > >> >> 4 files changed, 13 insertions(+), 13 deletions(-) > >> >> > >> >> diff --git a/app/test-pmd/csumonly.c b/app/test-pmd/csumonly.c > >> >> index 3d7d244..829e07f 100644 > >> >> --- a/app/test-pmd/csumonly.c > >> >> +++ b/app/test-pmd/csumonly.c > >> >> @@ -1080,11 +1080,12 @@ struct simple_gre_hdr { > >> >> ret = rte_gso_segment(pkts_burst[i], gso_ctx, > >> >> &gso_segments[nb_segments], > >> >> GSO_MAX_PKT_BURST - nb_segments); > >> >> + /* pkts_burst[i] can be freed safely here. */ > >> >> + rte_pktmbuf_free(pkts_burst[i]); > >> > > >> >It doesn't look correct to me. > >> >I think it should be: > >> >If (ret > 1) rte_pktmbuf_free(pkts_burst[i]); > >> > >> No, in original implementation, if gso failed, application will free it, > >> otherwise rte_gso_segment will free it (i.e. refcnt update -1 in > >> rte_gso_segment), this change will change previous behavior. application > >> will free it for both cases. > > > > > >That's the point - with current implementation: > >If ret == 1, then you shouldn't free input packet. > >Because in that case: > >input_pkt == output_pkt[0] > > > >And if you'll free it, you can't use it after it. > >In that particular case, you can't TX it. > > I checked gso code again, there are two cases even if ret == 1, one case is > it isn't segmented, the other is it is segmented but gso_do_segment returns > 1, for case #1, we can handle it as you said, but for case #2, we can't > handle it as you said because it has been segmented in fact. So I think we > should return 0 foe case #1 and don't do assignment "pkts_out[0] = pkt;", we > should handle case #2 as before, right? >
When will #2 case happen? In current implementation, ret of gso_do_segment() is > 1, when GSO happens; otherwise, ret is negative. It doesn't return 1. If you mean the case that pkt_len is smaller than gso_size, gso_do_segment() will not be called, since rte_gso_segment() will compare pkt_len and gso_size before. Thanks, Jiayu > > > >> > > > > >
